As for the Elves in Mirkwood, I still think we Bilbo will save the Dwarves, but then the Elves turn up and get rid of the rest of the spiders. Bilbo's story arc is about saving the Dwarves, and them learning to trust him. They can't remove a section out of his arc. Especially as the Dwarves start trusting Bilbo a lot more after Mirkwood.